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Lab 5.1: Configuring a Basic IPv4 Firewall

Lab 5.1: Configuring a Basic IPv4 Firewall



Scenario:
A host servcrIO requires protection by packet filtering.

Deliverable:
A set of IPv4 packet filtering rules in a custom chain called
class rules, allowing icmp and cups packets, state fuel
(ESTABLISHED,RELATED) replies, NEW packets connecting to sshd er packets will
and packets arriving on the loopback lo interface. All 0th be Logged before being REJECTed with icmp host prohibited

Instructions:
1. If necessary, connect to serverX as student and escalate your pnwlegcs t0 root with su

2. Ensure that the firewall is stopped, processing no rules.

3. Create a custom chain called class rules and insert a rule at the top of INPUT that jumps all packets to it. Save the firewall configuration when you are done.

4. Populate the class rules chain by editing etc, sys config, ip tables directly. Add rules that do the following

ACCEPT all traffic arriving on the loopback interface (10)
ACCEPT all packets that use the icmp protocol
ACCEPT all packets destined for both udp and top ports 631 (cups)

Hint
You will need two rules for this

5.  Load your new rules.
Flushing firewall rules
Setting chains to policy ACCEPT: filter
Unloading ip tables modules:
Applying ip tables firewall rules:

6.  On station ex, attempt to ssh to server ex. This should work.

Connect to cracker ex. remote . test and attempt to ssh to server ex. This should also work.

7.  Modify your rules to restrict ssh connections to only be accepted from other machines in the example . com network.

8.  On station ex, attempt to ssh to server ex. This should still work.

Connect to cracker ex. remote . test and attempt to ssh to server ex. This should no longer work.

9.  When done, Close your ssh sessions and termmal windows.

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